In one form of conventional variable speed pulley, a movable pulley sheave half is urged toward a fixed sheave half by a spring. When the V-belt received in the pulley groove defined by the confronting faces of the sheave halves is urged radially inwardly as by an increase in tension force applied in the belt, the belt overcomes the biasing force of the spring, permitting the movable sheave to move away from the fixed sheave and thereby reducing the effective diameter of the pulley, and thereby automatically varying the speed of the pulley driven by the belt.
It has further been known to provide means for axially moving the movable sheave half as a function of the speed of the pulley. One such structure is illustrated in Japanese Utility Model Patent No. 42-12433. As shown in the drawing thereof, a plurality of small spherical elements, such as ball bearings, are retained in a space confronting a radially inclined outer surface of the movable sheave. As the speed of the pulley increases, the spherical bodies are urged radially outwardly by centrifugal force and generate an axial force tending to urge the movable sheave so as to reduce the width of the belt receiving groove. Thus, the spherical elements augment the biasing force of the axially acting spring, whereby the total biasing force acting on the movable sheave is a composite of the spring force and the speed-related force generated by the spherical elements.
A serious problem, however, arises in the pulley structure of the Japanese Pat. No. 42-12433 in that the spherical elements tend to be heterogeneously distributed in the annular space in which they are contained. As shown in FIG. 4 of the Japanese Pat. No. 42-12433, when the pulley is at a standstill, the spherical bodies gravitate to the bottom of the space. When the pulley is rotated, the centrifugal force tends to maintain the spherical bodies in the same portion of the annular space, thereby generating vibrations and noise resulting from the unbalanced condition of the pulley. As rotation of the pulley is continued, the spherical bodies tend to move circumferentially of the annular space, and eventually may be disposed entirely circumferentially thereof. However, it has been found that there is a tendency for the spherical bodies to nonuniformly distribute themselves as a result of friction. Undesirable bridging occurs so that even after a substantial period of running of the pulley, vibration and noise continues.
The pertinent structure of the Japanese Pat. No. 42-12433 is illustrated in FIGS. 9 and 10 of the drawing hereof. As shown therein, the pulley structure includes a plurality of spherical force transmitting elements 5 which collect in a lower portion of the space 6 in which they are retained when the pulley is in a standstill position, as shown in FIG. 10. When the pulley is rotated, the centrifugal forces developed in the elements 5 tend to urge them toward an outer disposition, as shown in FIG. 9. It has been found, however, that the elements 5 do not uniformly redistribute themselves circumferentially about the outer portion of the space 6 and vibration and noise occur not only during speedup, but also during subsequent changes, as well as during steady state operation of the pulley. Thus, the pulley structure of Japanese Pat. No. 42-12433 has not proven fully satisfactory in use.
It is further known to mount the movable sheave half on the shaft for both axial and rotative movement. The biasing spring comprises a helical spring having one end connected fixedly to the shaft, and the opposite end connected fixedly to the movable sheave. In such an arrangement, the spring not only biases the movable sheave half toward the opposite sheave half, but also permits some angular displacement of the movable sheave half about the axis of the shaft so as to accommodate shock forces and the like generated in the operation of the belt drive. One example of such a pulley structure is illustrated in U.S. Pat. No. 4,626,227, of Hiroshi Takano, one of the inventors hereof, which patent is owned by the assignee hereof.